/*
 * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 *
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 *
 * (a) the Software, and
 *
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 *
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 *
 * This license is subject to the following condition:
 *
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.oracle.truffle.dsl.processor.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class Filterator<T> implements Iterator<T> {

    private final Predicate<T> includePredicate;
    private final Iterator<T> elements;

    private boolean hasCached;
    private T cached;

    public Filterator(Iterator<T> elements, Predicate<T> includePredicate) {
        this.elements = elements;
        this.includePredicate = includePredicate;
    }

    public boolean hasNext() {
        if (hasCached) {
            return true;
        }
        nextValue();
        return hasCached;
    }

    private void nextValue() {
        while (!hasCached && elements.hasNext()) {
            T element = elements.next();
            if (includePredicate.evaluate(element)) {
                cached = element;
                hasCached = true;
            }
        }
    }

    public T next() {
        T foundCached = getCached();
        if (foundCached != null) {
            return foundCached;
        } else {
            nextValue();
            if (!hasCached) {
                throw new NoSuchElementException();
            }
            return getCached();
        }
    }

    private T getCached() {
        if (hasCached) {
            hasCached = false;
            T value = cached;
            cached = null;
            return value;
        }
        return null;
    }

    @Override
    public void remove() {
        elements.remove();
    }

}
